The present invention relates to electrical primers and ignitors, and more particularly to an RF-insensitive semiconductor ignitor for use in firing ammunition rapidly and reliably.
Conventional small caliber shells employ mechanical or electrically initiated charge ignitors to create an ignition train which sets off the main propellant. Mechanical propelling charge ignitors are usually provided with percussion caps which are made to fire upon exposure to a mechanical impulse such as that caused by a firing pin or hammer blow. Electrically initiated charge ignitors, on the other hand, fire under the influence of a current pulse which may melt a resistive bridge wire, vaporize a metallic layer at an arc point, or pass through an electrically conductive charge.
A problem peculiar to conventional electrical ignitors is their sensitivity to electromagnetic (EM) radiation. EM fields may couple with an electrical propelling charge ignitor causing premature initiation. This problem is particularly acute aboard naval vessels which typically support multiple high power electromagnetic sources in close proximity to ordnance.
Various solutions to the problem of EM susceptibility, and the sensitivity of electroexplosive devices to RF fields in particular, are discussed in U.S. Pat. No. 5,085,146 to Baginski, which is hereby incorporated by reference. Baginski proposes a semiconductor device in which two p-n junctions have been created on top and bottom surfaces of a silicon substrate. Conductive layers atop the p-n junctions channel the firing current through the junctions, causing a small plug of conductive material on the top surface to vaporize. This generates a burst of hot plasma which ignites the primer mix and fires the propelling charge.
Applicants fabricated and tested a semiconductor ignitor which employs back-to-back Schottky diodes for use with the PHALANX CWIS 20-mm cartridge. As a consequence of these studies it was discovered that the back diode exhibits a tendency to short out when integrated into the PHALANX primer cup assembly. It was subsequently determined that similar failures could be produced by placing the semiconductor ignitor on a conductive sheet and exposing it to high pressures.